Sorry if this is a stupid question, but it doesn't seem immediately obvious how a thin strip of paper tape actually helps the mudding process in drywall installation except for perhaps reducing the amount of mud needed between panels.

This, from eHow:

Embedded in a layer of drywall joint compound, drywall tape creates a physical bond between adjacent sheets of drywall. Although the bond does not significantly contribute to the structural support of the drywall sheets, the bond reduces the movement and cracking of the sheets.

Wouldn't simply mudding between the joints have the same strength without the tape, albeit requiring more mud?

5 Answers
5

The problem with wood frame houses is that they shift in weird ways as the wind hits them and as the foundation settles. The 8 foot long side of a standard drywall panel has a LOT of mechanical force to it if it moves even somewhat independently of the sheet next to it, and the joint compound rapidly turns to powder without tape to back it up. The same can happen if there is too much or too little compound or the compound is the wrong type, you can also see this problem.

This is akin to the reason that drywall is gypsum between two sheets of paper... All you have to do to break or cut the gypsum is to disturb the paper.

The best practice I've seen/used is to use Durabond to bed the tape, and then normal green stuff over it to feather the joint.

The tape installed along the length of butt-joints (bridging the gap, approx ½ the width of the tape is attached to each board) in plasterboard is put there to help "prevent" cracks appearing along the joint lines.

Paper tape has a much higher shear strength than drywall plaster. Plaster can fill gaps, and smooth out the texture of the wall, but it's the drywall tape that holds it together as one seamless surface. Plaster isn't superglue; it needs a large surface area to provide adhesion , which is what the tape (several layers of it, usually) provides.

For surfaces that have a high chance of moving (less climate control, load-bearing wall, seams that have already cracked), drywall mesh works even better, but that is a little harder to smooth, and more expensive, so it's generally used only on problem areas.

Actually yes. There's usually at least two layers; a narrow "sealing" strip right over the joint, and then a wider "finishing" strip over that. Much like multiple layers of adhesive tape, it provides better adhesion, and it also results in a smoother overall look even though it is more layers of paper. The multi-layer approach is especially important on corners between walls and the ceiling, which generally move more as the house settles.
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KeithSAug 15 '11 at 21:12

7

Any links to back up using multiple layers of tape? I have never heard of it, never seen pro drywallers do it (in person or on TV) and can't find any references online to it. The typical method is single layer of tape (paper or mesh, mesh becoming more accepted and I've heard many pros say it's definitely better on butt joints, if not everything), and then 3 thin layers of mud, with pros generally preferring to mix their own, usually using sheetrock 90.
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gregmacAug 15 '11 at 22:07

I do punch-list for a busy builder... i have patched many many holes in walls (after having to move receptacles, after plumbers cut a hole in wall to make a repair ect... from 2"x4" to 10"x8'...).
I never use tape! Never had to go back and redo any patches!

I use durabond 20 min mud... and of course use strips of wood to screw my patch to before mudding!

A hole is one thing, since it should be all within the same piece of drywall. Tape is used in the joint between two pieces of drywall. And I have had to fix large cracks when builders have skipped this step. Very difficult to see when the place was just mudded, very easy to see when it's a year or two later.
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BMitch♦Sep 25 '14 at 14:51

Do you realize that the strips of wood that you use on your patches are reinforcing the join, exactly like tape between sheets of drywall.
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Niall C.♦Sep 25 '14 at 16:31

Way too many guesses here. Drywall tape serves a single purpose: To help make the seams invisible. That it! Drywall tape does not offer an mechanical strength at all. If you skipped the drywall tape and just used joint compound to fill in the seams, the seams would become visible again after the compound dried. Joint compound shrinks! Tape does not shrink! So applied tape first, and then joint compound.....results in a smooth finish because the compound doesn't need to be as thick (aka deep) because it rests on the smooth tape.

You claim there's guesses here then proceed to come up with your own guess. FYI, you can't apply the tape first. You have to have a layer of mud for the tape to adhere to. That initial application of mud does, obviously, fill in the gap as well.
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DA01Feb 7 '13 at 17:11